log files, where to look for....

After having not been able to use my X after a change of a video card any more I am looking for the reason why. Sax is not working and yast in console is not doing all the things I expect. I started looking into the various log files but have no idea where to find answers. Thought that warn and boot e.g would give me clues but to no avail. Found things which did not ring a bell like scpm which could find scdb whatever that is and gave an error. In warn I found a lot of things from which I thought they were working ok. Could somebody point me out reading material and mention log files which are really matter? -- NTReader v0.36w(P)/Beta (Registered) in conjunction with Net-Tamer.